1. Field of the Invention
This invention relates to a method suitable for forming a deposited film containing silicon, above all a non-single crystalline deposited film such as amorphous silicon (hereinafter called a-Si) or polycrystalline silicon useful as photoconductive film, semiconductor film or insulating film, etc.
2. Description of the Prior Art
In the prior art, as the method for forming a-Si deposited film by use of SiH.sub.4 or Si.sub.2 H.sub.6 as the starting material, there have been known the glow discharging deposition method and the heat energy deposition method. That is, they are the methods in which deposited films of a-Si are formed on the substrate by excitation-decomposition or polymerization of SiH.sub.4 or Si.sub.2 H.sub.6 by use of electric energy or thermal energy. Also, these films have been utilized for various purposes.
However, when SiH.sub.4 or Si.sub.2 H.sub.6 is used as the starting material, the influence of the discharged energy on the film during deposition under high power in the glow discharging method is great, whereby control under reproducible stable conditions can be performed only with difficulty. This is particularly the case when forming a thick deposited film with a broad area.
Also, in the heat energy deposition method, since a high temperature is required, the choice of substrate to be employed is limited. Further, the probability of elimination of the useful hydrogen atoms bonded in a-Si will be increased at high temperature, whereby desired characteristics are obtained only with difficulty.
Thus, when forming a deposited film by use of SiH.sub.4 or Si.sub.2 H.sub.6, it is difficult to ensure uniform electrical and optical characteristics as well as stability of the quality. Also under the present situation, there remain problems to be solved such as easy formation of surface disturbance of the film during deposition or defect within the bulk, etc.
Accordingly, in recent years, in order to cancel these problems, a light energy deposition method (light CVD method) employing SiH.sub.4 or Si.sub.2 H.sub.6 has been proposed and is attracting attention. According to such a light energy deposition method, due to the advantage that an a-Si deposited film can be prepared at low temperature, the above problems can be improved to a great extent.
However, according to such a light energy deposition method wherein SiH.sub.4 or Si.sub.2 H.sub.6 is used as the starting material under relatively small excitation energy such as light energy, no decomposition or polymerization with dramatically improved efficiency can be expected. Therefore, no improvement in film forming speed can be expected, thus posing a new problem of low bulk productivity.
The present invention has been made to cancel these problems under the present situation.